The use of polycarboxylic acids with or without catalysts in pad, dry and cure treatments to impart wrinkle resistance to cotton fabric was studied by Gagliardi and Shippee, American Dyestuff Reporter 52, p 300-303, (1963). They observed small increases in fabric wrinkle resistance after relatively long periods of heating, and noted larger fabric strength losses than are obtained with formaldehyde-based crosslinking agents. These excessive strength losses and the low yield of crosslinkages were attributed to the long heat curing times needed with the inefficient catalysts then available.
A more rapid and effective curing process for introducing ester crosslinks into cotton cellulose was described by Rowland et al, Textile Research Journal 37, p 933-941, (1967). Polycarboxylic acids were partially neutralized with sodium carbonate or triethylamine prior to application to the fabric in a pad, dry and heat cure type of treatment. Crosslinking of cellulose was obtained whenever the polycarboxylic acid contained three or more carboxyl groups suitably located in each molecule. With certain polycarboxylic acids, a useful level of wrinkle resistance was imparted. The conditioned wrinkle recovery angle was measured before and after five laundering cycles, and was found to decrease somewhat as a result of laundering, even though no loss of ester groups was detected. Neutralization of carboxyl groups with 2% sodium carbonate even at room temperature caused a 30% loss of ester groups. This indicates a lack of durability of the finish of alkaline solutions such as solutions of alkaline laundering detergents. The curing time needed in fabric finishing was moreover too long to permit high speed, mill-scale production.
Subsequently it was shown by Rowland and Brannan, Textile Research Journal 38, p 634-643, (1968), that cotton fabrics given the above cellulose crosslinking treatment with polycarboxylic acids were recurable. Creases durable to 5 laundering cycles could be put into the fabrics by wetting the latter, folding, and applying a heated iron. Evidence was obtained that the ester groups and adjacent unesterified hydroxyl groups on cotton cellulose.
These findings were elaborated by Rowland et al, U.S. Pat. No. 3,526,048. Sodium carbonate or triethylamine were again the examples of bases used to partially neutralize the polycarboxylic acid subsequently applied as the cellulose crosslinking agent. Rowland et al defined their process as requiring neutralization of 1% to 50% of all carboxylic acid functionality by a "strong base" selected from the group consisting of alkali metal hydroxides, carbonates, bicarcarbonates, acetates, phosphates and borates, prior to impregnating the fibrous cellulose with the aqueous polycarboxylic acid and heating to induce crosslinking. A strong base selected from the group consisting of ammonia and certain amines also was indicated as suitable for the partial neutralization of the polycarboxylic acid.
Stated limitations of the process of Rowland et al are that the process cannot be conducted with acids of fewer than three carboxyl groups per molecule, or with acids containing olefinic unsaturation or hydroxyl groups. The reasons were lack of reaction with cellulose chains for development of high levels of wrinkle resistance.
U.S. Pat. No. 4,820,307 to Welch et al discloses as cellulose crosslinking agents polycarboxylic acids which include aliphatic, alicyclic and aromatic acids. However, the acids are either olefinically saturated or unsaturated with at least three carboxyl groups per molecule or with two carboxyl groups per molecule if a carbon-carbon double bond is present alpha, beta to one or both carboxyl groups. An additional requirement is stated for esterifying cellulose hydroxy groups is that in an aliphatic or alicyclic acid a given carboxyl group must be separated by no less than 2 carbon atoms and no more than three. It is further stated that when two carboxyl groups are both connected to the same ring. The two carboxyl groups must be in the cis configuration relative to each other if they are to interact in a manner to form anhydrides which can esterify with cellulosic hydroxyl groups as proposed.
Surprisingly, according to the present invention, it has been discovered that effective crosslinking of the cellulosic hydroxyl group occurs with cyclic aliphatic polycarboxylic acids when two adjacent carboxyl groups are in the trans configuration.
U.S. Pat. No. 3,203,886 to Griffin discloses a photodimerization process for preparing the trans polycarboxylic acids used in the present invention.
It is understood that the term "wrinkle resistance" is defined pursuant to AATCC Method No. 66-1984, 1988. Technical Manual, American Association of Textile Chemists and Colorists, Research Triangle Park, N.C., which is herein incorporated by reference.